Junction Barrier Schottky Diode with Dual Silicides and Method of Manufacture

ABSTRACT

An integrated circuit, including a junction barrier Schottky diode, has an N type well, a P-type anode region in the surface of the well, and an N-type Schottky region in the surface of the well and horizontally abutting the anode region. A first silicide layer is on and makes a Schottky contact to the Schottky region and is on an adjoining anode region. A second silicide layer of a different material than the first silicide is on the anode region. An ohmic contact is made to the second silicide on the anode region and to the well.

BACKGROUND AND SUMMARY OF THE DISCLOSURE

The present disclosure relates generally to integrated circuits and,more specifically, to a junction barrier Schottky diodes (JBS) in theintegrated circuit.

Integrated circuits have generally included Schottky diodes for powerapplications. Schottky diodes tend to be very leaky at high reverse biasand high temperatures. Circuit designers have used junction barrierSchottky diodes to provide a solution to the leaky Schottky diodes. Thiscombination provides a Schottky-like forward conduction and PN diodelike reverse blocking of voltage. It basically includes a PN junctionand a Schottky junction diode in parallel. The formation of Schottkydiodes in integrated circuits generally uses the metal which forms asilicide with a silicon substrate that is used throughout the integratedcircuit. For example, the integrated circuit that requires a lowleakage, low forward bias drop Schottky diode, is typically manufacturedin a process which uses Titanium as the silicidation metal. Theresulting TiSi₂ is known to have a low barrier height which yields lowforward bias drop, but has higher reverse leakage than other silicides.In some applications it may be desirable to have a lower reverse leakagecurrent at the expense of higher forward bias voltage drop. To usedifferent silicides in the same fabrication process has historicallybeen avoided because of the cross contamination. The present disclosureprovides a method for implementing a dual silicide process without crosscontamination.

An integrated circuit of the present disclosure includes junctionbarrier Schottky diode which has an N-type silicon well having surface;a P-type anode region in the surface of the well; and a portion of thesurface of the well horizontally abutting the anode region being anN-type Schottky region. A first silicide layer is on the Schottky regionand an adjoining portion of the anode region. The first silicide layerforms a Schottky barrier with the Schottky region. A second silicidelayer of a different material than the first silicide layer is on theanode region. An ohmic contact is to the second silicide layer on theanode region, and an ohmic contact is to the well.

The first and second silicide layers are spaced from each other on theanode region. The well may include an N-type cathode contact region inthe surface having a higher impurity concentration than the Schottkyregion's impurity concentration, and the ohmic contact to the well is tothe cathode contact region or to portions of the second silicide layeron the cathode contact region. The well may include an N-type buriedlayer having a higher impurity concentration than the well's impurityconcentration and the N-type cathode contact region extends from thesurface to buried layer.

A method of manufacturing an integrated circuit having the junctionbarrier Schottky diode of the disclosure includes forming a P-type anoderegion in a surface of an N-type well; forming a first mask with anopening exposing an N-type Schottky region of the surface of the welland adjoining portion of the anode region; and applying a first materialwhich forms a first silicide layer of the first material with theexposed portions of the Schottky and anode regions. A second mask isformed with an opening exposing a portion of the anode region not havingthe first silicide layer; and a second material, different from thefirst material, is applied and forms a second silicide layer of thesecond material with the exposed portion of the anode region. An ohmiccontact is made to the second silicide layer on the anode region, and anohmic contact is made to the well.

The first and second silicide layers are formed spaced from each otheron the anode region. The method may include forming an N-type cathodecontact region in the surface having a higher impurity concentrationthan the Schottky region's impurity concentration. The second silicidelayer may be formed on the cathode contact region. The ohmic contact tothe well may be directly to the cathode contact region or to the secondsilicide layer on the cathode contact region. The well may include anN-type buried layer having a higher impurity concentration than thewell's impurity concentration; and the methods includes forming theN-type cathode contact region extending from the surface to buriedlayer, and forming the ohmic contact to the well to the cathode contactregion.

These and other aspects of the present disclosure will become apparentfrom the following detailed description of the disclosure, whenconsidered in conjunction with accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is cross-sectional view of an integrated circuit including ajunction barrier Schottky diode at a first mask stage of according to amethod of the present disclosure.

FIG. 2 is cross-sectional view of the integrated circuit after the firstsilicide stage of a method of the present disclosure

FIG. 3 is cross-sectional view of the integrated circuit at a secondmask stage of a method of the present disclosure

FIG. 4 is cross-sectional view of the integrated circuit after thesecond silicide stage of a method of the present disclosure

FIG. 5 is cross-sectional view of the integrated circuit after theinterconnect stage of a method of the present disclosure

FIG. 6 is cross-sectional view of another integrated circuit after theinterconnect stage of a method of the present disclosure.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 illustrates an integrated circuit 10 including a field effecttransistor FET 12 and a junction barrier Schottky (JBS) diode 14. AP-type silicon substrate 16 includes lateral oxide or field isolationregions 18 offering lateral isolation at the surface between variousdevices including the FET 12 and the JBS 14. The FET 12 is illustratedas including an N-type source 20 and drain 22 in the P-type substrate16. A gate 24 is separated from the channel region between the source 20and the drain 22 by a gate oxide 26.

The junction barrier Schottky diode 14 includes an N-type well 30 havingan optional buried N+ layer 32. A pair of P-type anode regions 38A and38B are formed in the surface of region of well 30. A Schottky region 40of the well laterally abuts the pair of anode regions 38. Region 38A mayalso abut Field 18 and the intervening region 40 will not be present.

After the formation of the source and drain regions 20 and 22, the gatestructure 24,26 and the anode regions 38A and 38B, the silicide processis begun. The integrated circuit is covered by a silicide blockingmaterial 50, for example a silicide blocking oxide. This may be in therange of 200 angstroms thick. A photo resist material 52 is applied andpatterned to form openings 54 exposing the Schottky regions 40 and aportion of the anode regions 38A and 38B. The portions of layer 50exposed by the opening of 54 are removed by, for example, etching. Photoresist 52 is removed and the wafer is cleaned.

The first silicide material is applied to the integrated circuit and onthe exposed surface regions of the well 30 and treated to form a firstsilicide 56 with the exposed silicon of the substrate. The applied firstmaterial which is not converted to a silicide is then removed. Theresulting structure is illustrated in FIG. 2. The first silicide 56 ison the Schottky region 40 as well as extending on to adjacent portionsof the anode region 38A and 38B. The remainder of the silicide blockinglayer 50 is shown as remaining on the substrate. In the present example,Cobalt may be the first material applied which will form silicide withthe Schottky region 40.

A second silicide blocking layer 60 is applied as illustrated in FIG. 3.Again, this may be an oxide in the range of 200 to 300 angstroms. Aphoto resist layer 62 is applied and openings 64 are formed. In additionto the exposed areas of the FET transistor 12, portions of the anoderegions 38A and 38B are exposed. Only the portion of the region notcovered by the first silicide layer 56 is exposed. This is importantbecause the two resulting silicide layers should be physically isolated.The exposed portions of silicide blocking masks 50 and 60 are removedby, for example etching, to expose surfaces of the surface area of thesubstrate to which the second silicide layers are to be applied. Thephoto resistance material 62 is removed and the wafer is cleaned. Asecond metal 66, different from the first metal 56, which forms silicideis then applied and treated to form a silicide with the exposed areas.This forms silicide layer 66 as illustrated in FIG. 4. The unreactedsecond metal is then removed. The second silicide 66 is separated fromthe first silicide 56 by the silicide barrier mask 50 on the anoderegions 38A and 38B.

In the present example, the second metal is Titanium which is typicallyused in integrated circuits. Titanium silicide is known to have a lowbarrier height which yields low forward bias drop and higher reverseleakage current then other silicide metals. The use of Cobalt silicideproduces a Schottky diode with higher forward bias drop but lowerreverse leakage current on the same chip. Although the example shown hasthe first silicide on the Schottky region 40 and the second silicide onthe FET 12 and the anodes 38, the second silicide may be provided on theSchottky region 40 of another Schottky structure on the same integratedcircuit. This will produce two different Schottky diodes on the sameintegrated circuits having different forward bias drops and reverseleakage currents.

The example applied Cobalt first because it has higher tolerances toelevated temperatures compared to Titanium. Thus, it is on theintegrated circuit longer and subject to more heating cycles. Anotherexample, where Titanium and Platinum are used as the two silicidemetals, the Titanium would be applied first and the Platinum would beapplied second. Other known metals which will form suicides may be used.Cobalt and Titanium are just two examples.

The process is then concluded with forming the remaining insulted layersand metal contacts. As illustrated in FIG. 5, the surface insulativelayer 70, for example, oxide and patterned with openings for contacts 72to the operative portions of the integrated circuit. Contacts 72A and72B are connected to source 20 and drain region 22, respectfully.Contacts 72C and 72D are made to the anode region 38A and 38B. An N-typecathode contact region 46, having a higher impurity concentration thanthe well 30, extends from the surface of the substrate down to theburied layer 32. Not shown in the previous process, the second silicidelayer 66 is formed on the surface of the cathode contact region 46. Itis separated from the first silicide region 56 by the mask 50. Contact72E is made to the cathode contact region 46 and the buried region 32.The parallel connection of the anode region 38A of the PN junction diodeand the anode region or the Schottky metal 56 of the Schottky diode isthrough the anode regions 38A and 38A. There is no metal contact 72directly to the first silicide 56.

It should be noted that the Schottky region 40 at the surface of thewell 30 has an impurity concentration so as to form a Schottky diodewith the first silicide material 56. Depending upon the material, theimpurity concentration of the Schottky region 40 may vary. They may beof a lower impurity concentration than the impurity concentration of thewell 30. Other modifications of the impurity concentration profile ofthe well structure 30 may be performed to increase the reverse blockingvoltage of the junction barrier Schottky diode.

As illustrated in FIG. 6, the cathode contact region 46 may not extendall the way down to the N buried layer 32, which may be eliminated ornot included in the well 30. Also in certain situations, the P anoderegions 38 may include P+ implant. This would prevent face-to-face orback-to-back Schottky diodes. A second implant 39 is illustrated in FIG.6. Although the anode region 38A and 38B are shown as two separateregions with abutting Schottky regions 40, the anode 38 may be a singlering. Also, the Schottky regions 40 may be a ring with a single anoderegion 38 in its interior. Although the present structure has beendescribed with respect to a junction barrier Schottky diode, the dualsilicide method may also be used with a single Schottky diode withoutthe PN diode.

Although the present disclosure had been described and illustrated indetail, it is to be clearly understood that this is done by way ofillustration and example only and is not to be taken by way oflimitation. The scope of the present disclosure is to be limited only bythe terms of the appended claims.

1. An integrated circuit including a junction barrier Schottky diode,the diode comprising: an N-type silicon well having surface; a P-typeanode region in the surface of the well; a portion of the surface of thewell horizontally abutting the anode region being an n-type Schottkyregion; a first silicide layer on the Schottky region and an adjoiningportion of the anode region, the first silicide layer forming a Schottkybarrier with the Schottky region; a second silicide layer of a differentmaterial than the first silicide layer on the anode region; and an ohmiccontact to the second silicide layer on the anode region, and an ohmiccontact to the well.
 2. The integrated circuit of claim 1, wherein thefirst and second silicide layers are spaced from each other on thesurface.
 3. The integrated circuit of claim 1, wherein the well includesan N-type cathode contact region in the surface having a higher impurityconcentration than the Schottky region's impurity concentration, and theohmic contact to the well is to the cathode contact region.
 4. Theintegrated circuit of claim 3, wherein the well includes an N-typeburied layer having a higher impurity concentration than the well'simpurity concentration and the n-type cathode contact region extendsfrom the surface to buried layer.
 5. The integrated circuit of claim 3,wherein a portion of the second silicide layer is on a portion of thecathode contact region and the ohmic contact to the well is to theportion of the second silicide layer on the cathode contact region. 6.The integrated circuit according to claim 1, wherein the first silicidelayer is Cobalt silicide and the second silicide layer is a Titaniumsilicide.
 7. The integrated circuit according to claim 1, wherein thefirst silicide layer is Titanium silicide and the second silicide layeris a Platinum silicide.
 8. A method of manufacturing an integratedcircuit including a junction barrier Schottky diode, the methodincluding: forming a P-type anode region in a surface of an N-type well;forming a first mask with an opening exposing an N-type Schottky regionof the surface of the well and adjoining portion of the anode region;applying a first material and forming a first silicide layer of thefirst material with the exposed portions of the Schottky and anoderegions; forming a second mask with an opening exposing a portion of theanode region not having the first silicide layer; applying a secondmaterial different from the first material and forming a second silicidelayer of the second material with the exposed portion of the anoderegion; and forming an ohmic contact to the second silicide layer on theanode region, and an ohmic contact to the well.
 9. The method of claim8, wherein the first and second silicide layers are formed spaced fromeach other on the surface.
 10. The method of claim 8, includes formingan N-type cathode contact region in the surface having a higher impurityconcentration than the Schottky region's impurity concentration, and theohmic contact to the well is to the cathode contact region.
 11. Themethod of claim 10, wherein the well includes an N-type buried layerhaving a higher impurity concentration than the well's impurityconcentration, and including forming the N-type cathode contact regionextending from the surface to buried layer.
 12. The method of claim 10,includes forming a portion of the second silicide on the cathode contactregion on a portion of the cathode contact region, and the ohmic contactto the well is formed to the second silicide layer on the cathodecontact region.
 13. The method of claim 8, wherein the first material isCobalt and the second material is Titanium.
 14. The material of claim 8,wherein the first material is Titanium and the second material isPlatinum.